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136 votes
Accepted

Why did MS-DOS applications built using Turbo Pascal fail to start with a division by zero error on faster systems?

Turbo Pascal programs start by calibrating a delay loop (so that the Delay function knows how much to spin to achieve a certain delay). The calibration counts the number of times a certain loop is run ...
  • 98.2k
127 votes

Why did some old MS-DOS games lack the ability to exit them?

Paratrooper was originally a “PC booter”. All PC booters run without DOS or any other operating system¹ — to start them, you would insert the floppy into the drive, and switch the computer on (or ...
  • 98.2k
121 votes
Accepted

What character is the MS-DOS cursor?

The text-mode cursor isn’t a character, it’s managed separately by the video output circuitry (which is how it keeps blinking even when your computer is busy or locked up). It can be enabled or ...
  • 98.2k
105 votes
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On DOS computers, what would the PARK command do?

Hard drives have read/write heads which fly above the spinning disks when the drive is powered. When power is removed, the heads no longer fly... For a long time now, the arms which hold the heads ...
  • 98.2k
104 votes
Accepted

Why did IBM make the PC BIOS source code public?

In the late '70s and very early 80s it was not unusual to make BIOS source code available. Apple did indeed do so; the full source listing starts at page 76 of the Apple II Reference Manual. Atari did ...
  • 22.2k
100 votes

Was there ever any reason to wait 30 seconds to restart a c.1995 PC?

I am an EE system designer. I have designed many PC systems (and non PC ones). I do lots of power supply work and have dealt with many HDDs. As always, there is bound to be an exception somewhere. ...
  • 1,009
94 votes

Why weren't bootable game disks ever common on the IBM PC?

Bootable game disks do exist for the IBM PC. Conflict in Vietnam is an example of such a game. As can be seen on page 8 of the manual, the game boots directly without loading DOS first. The main ...
  • 14.1k
93 votes
Accepted

Why do PCs boot in 720x400 resolution?

This is historically not uncommon at all. Before starting an Operating System and initializing a graphics mode, your PC operates in the simplest display mode available, 80×25 text mode. The original ...
  • 1,455
87 votes
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Why does NumLock exist?

My keyboard has over a hundred keys on it. But there's one labelled "NumLock". Simply because the dedicated cursor keys were not there to begin with. As seen here with the original PC Model ...
  • 177k
81 votes
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Who set the 640K limit?

There was a 640K limit on the original IBM PC, but it was the result of IBM’s design decisions, and nothing to do with Microsoft: it’s the largest contiguous amount of memory which can be provided ...
  • 98.2k
76 votes
Accepted

What did the 'turbo' button actually do?

The Turbo button originally adjusted the clock speed of the computer between the full speed of the machine and a slower speed intended to be compatible with something more industry standard. It wasn't ...
  • 4,356
74 votes

Why did the IBM PC need a sound card?

The original IBM PC and later variants used an Intel 8253 or 8254 as a sound chip. The 8253 is a timer circuit, containing three timers able to generate timed interrupts or square-wave output with ...
  • 177k
71 votes

Why did IBM make the PC BIOS source code public?

When other manufacturers attempted to copy the BIOS from the source listings, IBM sued them for copyright violation and won. Besides, even without the listings, anyone would have been able to dump ...
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71 votes
Accepted

What is the "two-drive trick" that can read Amiga disks on a PC?

This only works with 2 drives on the same controller and cable. The floppy controller doesn't know when the disk (hardware) has been switched on the port (software), so a transfer command can be ...
64 votes
Accepted

Why does DOS ask for the current date and time upon booting?

Because it used to be necessary. While a battery-powered real-time clock is standard today, this wasn’t always the case. The very first IBM 5150 did not include an RTC chip; the system clock was ...
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63 votes
Accepted

Is it true that control+alt+delete only became a thing because IBM would not build Bill Gates a computer with a task manager button?

The answer to the question as written is no. However, I can see where it came from. When Microsoft developed Windows NT, they decided they needed a "secure attention key" (SAK). This was a key, or ...
  • 10.4k
62 votes

Locked-up DOS computer beeped on keypress. What mechanism caused that?

Well, it was simply the BIOS' way to tell you that the keyboard buffer is all the way filled up. What was actually "counting" my keypresses? In so far as there is a 16 entry (32 bytes) buffer area ...
  • 177k
61 votes

Why was the return key symbol ↵ drawn differently from the motion of a CR-LF?

Even though the CR usually goes before the LF in ASCII text, most printer mechanisms actually perform the LF before, or during, the CR. So the shape of the arrow is actually accurate. This is even ...
  • 16.1k
60 votes

Why were some early PC 3D cards unsuitable for 2D graphics?

Early high-performance 3D accelerators such as the Voodoo Graphics have limited framebuffer resolutions (640×480 for most Voodoo Graphics configurations, 800×600 for the Voodoo2 in non-SLI) and colour ...
  • 98.2k
55 votes

Was there ever any reason to wait 30 seconds to restart a c.1995 PC?

The reset button does not affect the power supply at all. It sends a reset signal to the CPU (and probably the bus). Some power supply designs indeed will wear quicker if quickly switched on and off, ...
55 votes
Accepted

Did John Carmack really invent "Adaptive Tile Refresh"?

John Carmack almost certainly was the first to use the hardware scrolling capabilities of the EGA specifically, together with efficient tile and sprite drawing and erasing algorithms to create a slick,...
  • 10.2k
54 votes
Accepted

What were the real competitors to the early IBM PC?

The 80s weren't homogeneous computing-wise. I'd break it down into roughly 3 eras: Early 80s: Atari, Commodore, Radio Shack, and Sinclair 8-bit machines (and their clones) were the most common in ...
  • 9,010
53 votes

What character is the MS-DOS cursor?

The cursor on the CGA, MDA, EGA, and VGA cards was a hardware sprite generated on the earlier cards by the 6845 video controller, and on later cards by a chip that emulates the 6845. That chip has an ...
  • 29.2k
53 votes
Accepted

Did IBM encourage Bill Gates to retain the rights over PC-DOS?

TL;DR: It was IBM's idea. IBM never intended to buy any of the software they acquired for the PC - and MS never intended to supply any OS beside Xenix. But MS (Paul Allen) soon recognized the ...
  • 177k
53 votes

What caused older computer fans to be so much louder than they are today?

Maybe heatsink technology made progress, but one of the reasons is adaptative fan speed. Modern PCs have temperature sensors on main chips, and the firmware of the boards (or the BIOS, or UEFI, ...
50 votes
Accepted

What makes a floppy disk bootable?

The notion of a bootable-vs-non-bootable floppy is a little odd. It's worth noting that almost all floppies you're likely to have are actually bootable: it's just that they boot a program that isn't ...
  • 12.5k
50 votes

Why doesn’t my VGA-to-HDMI converter work with my 286 PC?

The manual says that the smallest resolution it can handle is 800x600. That is almost certainly the key. Original VGA supported 640x480 16-colors and 720x400 (essentially a small step up from the ...
46 votes
Accepted

Looking for PC graphics demo software from the early 90s called "Unreal"

Unreal Megademo, Future Crew, 1992 possibly? Certainly has all the elements you mention.
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46 votes
Accepted

Did any PC software floating point use non-IEEE format?

Turbo Pascal 2.x and the "ordinary" version of Turbo Pascal 3.x used a six-byte floating-point format which offered higher precision than an IEEE single-precision float, offering the ...
  • 29.2k

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